The stored messenger RNA of sea urchin eggs is not translated until after fertilization through m RNA, ribosomes, and other factors are all present in the egg. This observation has led to the hypothesis that such m RNA is "masked". Our current studies are directed at testing this hypothesis. We have found that m RNA is present in eggs in the form of ribonucleoprotein particles, and that this RNA is not translatable unless protein is removed from the particles. We are investigating the proteins of the egg RNP's and are comparing non-translatable egg particles with the translatable m RNP particles of embryo polysomes. We are also examining the flow of stored m RNA into polysomes in embryos as well as translation rates of such m RNA's. BIBLIOGRAPHIC REFERENCES: Raff, R. A., K. M. Newrock, R. D. Secrist, and F. R. Turner, "Regulation of Protein Synthesis in Embryos of Ilyanassa Obsoleta," Amer. Zool., Vol. 16 (1976), pp. 529-545. Raff, R. A., "The Molecular Determination of Morphogenesis," Bio Science, (July, 1977), Vol. 27, pp. 394-401.